The present invention relates to medical stimulation systems, e.g., a spinal cord stimulation system. More particularly, the invention relates to medical stimulation leads that include lead fixation means, i.e., ways to ensure that the lead, once implanted, does not move away from its desired implant location.
Spinal cord stimulation (SCS) is a well accepted clinical method for reducing pain in certain populations of patients. SCS systems typically include an implanted pulse generator, lead wires, and electrodes connected to the lead wires. The pulse generator generates electrical pulses that are delivered to the dorsal column fibers within the spinal cord through the electrodes which are implanted along the dura of the spinal cord. In a typical application, the attached lead wires exit the spinal cord and are tunneled around the torso of the patient to a subcutaneous pocket where the pulse generator is implanted.
When an electrical pulse or sequence of pulses is applied to a selected electrode or combination of electrodes, the patient typically experiences a “paresthesia” (usually manifested as a mild tingling sensation) that is therapeutic, i.e., relieves the pain or other discomfort that the patient is experiencing.
Spinal cord and other stimulation systems are known in the art. For example, in U.S. Pat. No. 3,646,940, there is disclosed an implantable electronic stimulator that provides timed sequenced electrical impulses to a plurality of electrodes so that only one electrode has a voltage applied to it at any given time. Thus, the electrical stimuli provided by the apparatus taught in the '940 patent comprise sequential or non-overlapping stimuli.
In U.S. Pat. No. 3,724,467, an electrode implant is disclosed for the neuro-stimulation of the spinal cord. A relatively thin and flexible strip of physiologically inert plastic is provided with a plurality of electrodes formed thereon. The electrodes are connected by leads to an RF receiver, which is also implanted, and which is controlled by an external controller. The implanted RF receiver has no power storage means and must be coupled to the external controller in order for neurostimulation to occur.
In U.S. Pat. No. 3,822,708, another type of electrical spinal cord stimulating device is shown. The device has five aligned electrodes which are positioned longitudinally on the spinal cord and transversely to the nerves entering the spinal cord. Current pulses applied to the electrodes are said to block sensed intractable pain, while allowing passage of other sensations. The stimulation pulses applied to the electrodes are approximately 250 microseconds in width with a repetition rate of from 5 to 200 pulses per second. A patient-operable switch allows the patient to change which electrodes are activated, i.e., which electrodes receive the current stimulus, so that the area between the activated electrodes on the spinal cord can be adjusted, as required, to better block the pain.
Other representative patents that show spinal cord stimulation systems or electrodes include U.S. Pat. Nos. 4,338,945; 4,379,462; 4,519,403; 5,121,754; 5,417,719 and 5,501,703. Each patent is incorporated herein by reference.
U.S. Pat. No. 5,733,322, also incorporated herein by reference, discloses a positive fixation percutaneous epidural neuro-stimulation lead that utilizes an extension that extends distally beyond the most distal electrode. The extension is held in place by contact with both the dura and spinal canal wall so that lateral lead migration of the electrodes is minimized. Other electrode fixation techniques are taught, e.g., in U.S. Pat. No. 4,418,697, which describes an adhesive (putty) to fixate electrodes to the skin; and in U.S. Pat. No. 4,282,886, which describes an adhesive adapted to attach an electrode to the epicardium. Both the '697 and the '886 patents are likewise incorporated herein by reference.
On a daily basis, patients change posture during sitting, bending, sleeping, walking or other activities that cause implanted neural stimulation leads to flex and move. Disadvantageously, when a neural stimulation lead chronically or temporarily moves, it can affect the treatment results. For example, an SCS lead that moves up, down or rotates to the side of the spinal cord can result in therapy no longer being adequate to attain the desired paresthesia, thereby rendering the SCS system incapable of performing its intended function. When a lead moves temporarily, the lead movement may thereafter require an adjustment to the delivered stimulation energy, e.g., a reduction of the stimulation output or an increase of the stimulation output. In some instances such adjustment of the stimulation energy may not be possible, thereby rendering the SCS system less effective or even ineffective for its intended purpose. In the worst case scenario, the patient must submit to a surgical procedure to manually adjust the location of the lead in order to regain effective SCS system operation.
Thus, it is seen that maintaining the correct lead position is critical, and an undesirable movement of the lead can render the SCS, or other neural stimulation system, ineffective and useless. What is needed are lead designs that (1) chronically fixates the lead to its desired location, e.g., to the dura in the case of an SCS system; and (2) fixates the lead in a manner that provides adequate lead flexibility to accommodate postural changes.